Treatment of hydrocarbon oils



Patented Apr. 10, 1934 UNITED STATES TREATMENT. OF HYDROCARBON OILSJacque G. Morrell, Chicago, 111., assignor to Universal Oil ProductsCompany, Chicago, 111., a corporation of South Dakota No Drawing.Application June 6, 1931, Serial No. 542,704

4 Claims.

This invention relates to the treatment of hydrocarbon oils and refersmore particularly to the treatment of the relatively low boilingfractions resulting from the cracking of heavier hydrocarbons thoughsimilar distillates produced from noncracking distilling operations mayalso be treated.

In a more specific sense the invention has reference to the treatment ofhydrocarbon oil fractions of the types mentioned with reagents adaptedto reduce their content of unsaturated hydrocarbons and sulphurcompounds, a process being hereinafter disclosedwhich possesses markedad- I; vantages over processes at present in vogue for producing similarresults.

In its specific and preferred embodiment the invention comprisestreatment of hydrocarbon oil vapors with pyrosulphates, or the salts ofpyrosulphuric acid, e. g., the pyrosulphates of sodium,

potassium or ammonium. It is also contemplated using mixtures of aqueoussolutions of pyrosulphates and sulphuric acid. The use of possiblepyrosulphates of the heavy metals is also contemplated.

As a result of extended researches in the different branches of the oilrefining industries it has been definitely established that low boilinghydrocarbon distillates containing large amounts of fractions boilingwithin therange of commercial gasoline are composed of, in addition tohydrocarbons of a saturated nature such as paraffins and naphthenes,varying though usually minor portions of unsaturated hydrocarbons bothof the straight chain and cyclic types. The unsaturated compounds,particularly those of the straight chain type, are characterized by atendencyto polymerize under the influence of light and air or otheroxidizing agents to form high boiling resinous or tarry aggregates whichcolor the distillates and depreciate the value of the gasoline producedtherefrom both from the standpoint of selling and from the standpoint ofits use as motor fuel. The sulphur content must usually be down to acertain limit value to correct undue corrosion effects. To reduce thepercentage of the more reactive unsaturated and. sulphur compoundsmentioned and to render the derived motor fuels sufficiently stable hasbeen the object of a large number of refining methods, the first andmost generally used of which being the well known treatment withsulphuric acid of commer-- cial grade, either alone or combined withother alkaline or sweetening treatments. The use of sulphuric acid,however, to selectively remove the more highly unsaturated olefins whichare the principal gum-formers while leaving unaffected the mono-olefinswhich add to the antiknock value of the fuel without adding materiallyto the gum content, is attended with difficulty owing to the lack ofcomplete selectivity of the acid in respect to the separation mentioned.It is with improvements in the ordinary methods of treating gasolinedistillates particularly cracked distillates, that the present inventionis concerned, the use of the pyrosulphates mentioned affording a moreselective and readily controllable treating method.

Persulphuric acid of the formula H2S2O'z may be considered as a compoundbetween one molecule of water and two molecules of sulphur trioxide, andcorresponding to a sulphuric acid containing free sulphur trioxide byweight. It is a crystaline solid melting at 35 C., the melting pointbeing lowered either by the addition of sulphur trioxide or water.Numerous salts of this acid have been prepared, the most common of whichare those of sodium and potassium, these being best prepared by theaction of sulphur trioxide upon their anhydrous normal sulphates. Sodiumpyrosulphate Na2S2O7 has a melting point of 400 C. and a density of2.66. The melting point of the potassium salt is slightly higher being414 C. while its density is slightly lower, that is, 2.51. In additionto the two simple salts mentioned the existence of the following doublesalts has been confirmed:

While treatment of cracked vapors by pyrosulphates may be efiected in avariety of ways, a few will be mentioned as indicating the wideapplicability of these compounds. A convenient method of use consists inincorporating the salt to be used with spacing or adsorbent materialsuch as fullers earth and other earthy and relatively inert materialsand placing the finely divided composite mass in a tower or columnthrough whichthe vapors may pass upwardly or downwardly depending uponoperating conditions encountered such as, for example, the quantity andtype of sludge formed. The melting points of the salts most commonlyemployed, that is, those of sodium, potassium and ammonium areconsiderably above the temperatures of fractionated cracked vapors asthey are encountered in practice but the melting pointof the sludgesproduced in some cases is sufiiciently lower to permit their flow underconditions of operation in vapor phase treatments, so that the reactionproducts may be more or less continuously removed from the spacingmaterial as liquid during the operation of the process. Itlis within thescope of the invention to employ a number of treating towers in parallelso that cracked vapors from any source may be continuously treated, atower containing fresh treating reagent being cut in as other towersbecome spent.

Treatments of cracked vapors may also be conducted in towers or columnscontaining no filling material by injecting finely divided compositeparticles containing pyrosulphates into the upper portions of suchtowers so that they gradually settle downwardly through the risingsteamof vapors and efiect a countercurrent treatment, the sludge-coatedparticles being removed from the bottom of the tower eitherintermittently or continuously by the use of suitable mechanical devicessuch as belt or screw conveyors.

Solutions of pyrosulphates, preferably aqueous solutions may be employedby countercurrent or concurrent treatment of the hydrocarbon vapors. Itis also within the scope of this invention to mix solutions ofpyrosulphates with sulphuric acid as a treating agent. It is to beunderstood that the solids and solution will vary somewhat in degree oftreating efiect produced as well as results and hence are not to beconsidered as precise equivalents.

Temperatures and pressures employed in such vapor phase treatments ashave been described above may be determined to some extent by thepressures and temperatures existing in the fractionating equipment fromwhich the vapors are produced though at times such temperatures andpressures may need to be reduced in order to minimize undesirable sidereactions resulting from the tendency of the pyrosulphates to oxidizewhen temperature and pressure conditions are permitted to attain acertain degree of severity. The temperature of cracked vapors from theprimary fractionating equipment of cracking processes are commonlyincluded within the range of 250 to 550 F. and the pressures arecommonly from 100 to 500 pounds per square inch. To effect finalfractionation for the production of vapors of approximate gasolineboiling point range the pressure is frequently reduced to below 100pounds per square inch with a corresponding drop in temperature due toadiabatic expansion.

Use of pyrosulphates in the treatment of cracked vapors is mostadvantageously preceded by alkaline or metallic treatments to removehydrogen sulphide and a certain amount of highly reactive sulphurderivatives though this is not absolutely essential to the efiicientoperation of the process. The use of these salts may also be followed bythe addition of ammonia to neutralize traces of residual acidiccompounds and the further passage of the vapors through filter beds toremove minor amounts of entrained reaction products.

The degree and nature of treating effects produced may be readilycontrolled by selection of the particular salt to be used and the amountof inert material with which it is incorporated as well as by themanipulation of pressure and temperature and the use of upward and downflow, etc. At times the double salts mentioned in the precedingparagraph or combinations of salts may be used and also salts of lessbasic elements 7 than the sodium and potassium and other alkali metals.

As an example of results obtainable by the use of the process of theinvention a case involving the treatment of the vapors from the crackingof a mixture composed of 50% of Mid-Continent residuum and 50% of aheavy gas oil may be considered. The vapors from a cracking plantoperating on such a blend at approximately 250 pounds per square inchand a temperature of 935 F. may be fractionated in a secondaryfractionator under the reduced pressure of approximately 75 pounds persquare inch to produce a frac tion with a final boiling point ofapproximately 400 F. which if condensed and given no other treatmentthan a light caustic wash may have the following approximatecharacteristics:

Gravity 55.5 Mgs. gum by copper dish method 400 Sulphur 0.25% Color Paleyellow By treating the vapors with fullers earth containing 10% byweight of sodium pyrosulphate so that approximately 6 pounds of the saltare consumed per barrel of condensate and following this treatment byproper neutralization and washing to remove traces of entrained reactionproducts, the gasoline finally condensed may have the followingproperties as compared with the above:

Gravity 55.8 Gum -25 mgs. Color Sulphur 0.1

A comparison of the properties of the raw gasoline with the gasolineproduced by treating acl cording to the process of the invention willreadily indicate the advantages to be gained by the use of the process.Similar results may be obtained with Californian and other chargingstocks. It will be noted also that the amount of sodium py- 1 rosulphateused by weight is approximately equal to the weight of sulphuric acidwhich would ordinarily be employed in liquid phase treatment of the rawgasoline prior to its rerunning to produce a finished product. However,since the percent- 1 age of sulphur trioxide in sodium pyrosulphate isonly 36% compared with 81.6% in sulphuric acid it will be evident thatthe treating effects in the present instance are produced by the use ofconsiderably lessened amounts of acidic material. 1

The improvements in treating process constituting the present inventionwill be obvious from the preceding descriptive material and example butthe points covered are more or less descriptive and illustrative and theparticular details dis- 1 closed are not to be considered asconstituting a limitation upon the generally broad scope of theinvention.

I claim as my invention:

1. A process for refining hydrocarbon distillates which comprises,subjecting said distillate in heated vaporous condition to the action ofan aqueous solution of a pyrosulphate.

2. A process for refining hydrocarbon distillates which comprises,subjecting said distillate 1 in heated vaporous condition to the actionof an aqueous solution containing a pyrosulphate and sulphuric acid.

3. A process for refining hydrocarbon distillates which comprises,subjecting said distillate in heated vaporous condition to the action ofan aqueous solution containing a pyrosulphate.

4. A process for refining hydrocarbon distillates which comprises,subjecting said distillate in heated vaporous condition to the action ofan aqueous 1 solution containing a pyrosulphate of an alkali metal.JACQUE C. MORRELL.

